Closure for open-headed medical implant

ABSTRACT

A closure for an open headed medical implant, such as a bone screw. The closure having a cylindrical body having an axis of rotation and also having a radially outer surface with a thread or other guide and advancement structure thereon. The body having a plurality of apertures that open onto a top surface of the body and that are parallel to but spaced from the axis of rotation. The closure also has a break-off head centrally attached by a neck to the top surface of the body.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. Ser. No. 13/694,970, filed Jan. 23, 2013, which is a continuation of U.S. Ser. No. 10/142,614, filed May 9, 2002, now U.S. Pat. No. 8,377,100 which was a continuation-in-part of U.S. Ser. No. 10/014,434 filed Nov. 9, 2001, now U.S. Pat. No. 6,726,687, issued Apr. 27, 2004 which was a continuation-in-part of U.S. Ser. No. 09/732,528, filed Dec. 7, 2000, now U.S. Pat. No. 6,454,772, issued Sep. 24, 2002.

BACKGROUND OF THE INVENTION

The present invention is directed to an open headed medical implant and, in particular, to a closure for closing the head of an open headed bone screw, hook or the like.

Bone screws are used especially in spinal surgery to support and position various implants needed to repair a spine that has suffered injury, illness or genetic defect. Bone screws of this type are screwed into the vertebrae of the spine and have a head that projects outside the bone which receives other implants, such as rods, that extend along the spine. Bone screws are of two general types which are either open headed or closed headed. Hooks and certain other implants also sometimes have open heads. The present application is directed to open headed bone screws and related implants such as hooks and the like that have such an open head to receive another implant.

In open headed bone screws and related implants, the head includes two upright arms that form a channel therebetween. The channel is sized to receive a rod or the like and is open to make it easier to place the rod in the head. The rod must then be tightly held or locked in the head to prevent relative movement between implants after the surgery. To hold the rod in the head, plugs have been used that are screwed into threads on the interior surfaces of the arms.

The present invention is directed especially to improvements in such plugs or closures that make them easier to insert in the head, that better ensure that the plug effectively secures the rod so that the rod does not later slip, that allow the plugs to be easily removed should the overall implant system require rearrangement and which provide a comparatively low profile, so as reduce trauma and irritation to the surrounding tissues of the patient.

SUMMARY OF THE INVENTION

A closure is provided for an open headed implant, especially a bone screw or hook for use in spinal surgery. The closure has a cylindrical shaped body with an axis of rotation. The body has a radially outer surface that has a thread or other guide and advancement structure thereon that is sized and shaped to be received in mating threads or structure on interior surfaces of arms of the implant head. The closure is operably rotated and advanced into the head of the implant to capture a rod or other part of an overall spinal support system. The closure captures and locks such a rod in position relative to the implant to prevent rotation or axial movement between the joined parts.

The closure body has a top surface and a bottom surface with a plurality of cylindrical bores extending parallel to the axis of rotation into the body from the top surface or other removal apertures. The bores or apertures are positioned in spaced relationship to one another and to the axis of rotation. The bores or apertures are sized and shaped to cooperatively mate with posts on a tool to allow removal of the closure from the implant after insertion, should such be necessary.

The closure also includes a break-off head centrally mounted by a neck on the top surface of the body. The break-off head is adapted to receive a socket tool and be rotated thereby during installation. The break-off head is also designed to break from the body at a torque limiting or break-off region or location which is preferably whereat the neck intersects with the top surface of the body, when a preselected torque is applied to the break-off head. When the break-off head is broken away, the bores or apertures become exposed and are mateable with a removal tool should it become necessary to remove the closure.

Objects and Advantages of the Invention

Therefore, the objects of the present invention are: to provide a closure for an open ended implant that provides a plurality of spaced removal apertures that are offset from an axis of rotation of the closure and that cooperate with a tool to allow removal of the closure; to provide such an implant having a closure with a break off head for mating with an insertion tool for inserting the closure into the implant; to provide such an implant wherein the removal apertures are not accessible for effective access, when the closure is in the implant until the break-off head is broken away; to provide such an implant that strongly grips a rod or the like received in the implant and that provides a relatively low profile; and to provide such an implant and closure therefor that is relatively easy to use, comparatively easy to produce and is especially well suited for the intended use thereof.

Other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention.

The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a bone screw type implant and closure in accordance with the present invention prior to insertion of the closure into a head of the bone screw.

FIG. 2 is a fragmentary side elevational view of the bone screw with a rod and the closure received therein and with a tool being utilized to insert the closure and provide torque to the break-off head of the closure and further with the bone screw shown embedded in a bone that is indicated by phantom lines.

FIG. 3 is a fragmentary and exploded side elevational view of the bone screw, rod and closure with the break-off head of the closure being shown broken therefrom.

FIG. 4 is a fragmentary top plan view of the bone screw, rod and closure with the break-off head removed.

FIG. 5 is a top plan view of the closure with the break-off head broken therefrom, but shown in phantom.

FIG. 6 is a bottom plan view of the closure.

FIG. 7 is an exploded and fragmentary side elevational view of the bone screw, rod and closure showing a removal tool positioned above the closure.

FIG. 8 is a fragmentary and enlarged view of the bone screw, rod and closure shown in FIG. 7 with the removal tool inserted into the closure and with portions of the bone screw and closure broken away to show detail thereof.

DETAILED DESCRIPTION OF THE INVENTION

As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure.

The reference numeral 1 generally indicates a medical implant in accordance with the present invention. The implant 1 includes a bone screw 5, a closure 6 for the bone screw 5 and a rod 7. The implant 1 is received in a vertebrae 9, typically in conjunction with other implants that are not shown. The closure 6 also functions in conjunction with other open-headed implants, such as hooks and the like.

The bone screw 5 includes a shank 12 and a head 13. The shank 12 is threaded with a coarse helicably wound flighting-like thread 16 that is threaded into the vertebrae 9, so as to secure and support the bone screw 5 and allow the head 13 to extend from the vertebrae 9.

The bone screw head 13 includes a base 20 with a pair of upstanding spaced arms 21 and 22 on opposite sides of the base 20 forming a generally U-shaped configuration, when viewed from the side, and defining a channel 23 therebetween. The channel 23 is sized and shaped to receive the rod 7.

The arms 21 and 22 each include an interior surface 26 and 27 respectively. The interior surfaces 26 and 27 have a guide and advancement structure which in the illustrated embodiment is a partial helical wound thread 29 on each. While the illustrated thread 29 is a conventional V-shaped thread, the purpose of this thread is to engage similar threads on the closure 6 to guide the closure 6 relative to the bone screw 5, as discussed below, and to provide for biased advancement of the closure 6 along the central axis A thereof relative to the bone screw 5 upon rotation of the closure 6. It is foreseen that other structures including other types of threads, such as buttress and reverse angle threads, and non threads, such as helical wound flanges or the like having interlocking surfaces, could be alternatively used for this purpose. Therefore, the illustrated internal partial or discontinuous threads on the bone screw arms 21 and 22 along with the mating thread on the closure 5 provide guide and advancement structure that operably positions and advances the closure 6 relative to the bone screw 5 during installation. The threaded surfaces 26 and 27 are spaced and not connected so as to present only a partial threadform which each face one another and cooperate with the closure 6, as is noted below. In the illustrated embodiment, the threaded surfaces 26 and 27 extend from a top 30 of the bone screw 5 only partially down the arms 21 and 22.

The closure 6 includes a body 35 and a torque limiting break-off head 36. The closure body 35 is generally cylindrical in shape and has a radially outward external surface 40 that extends 360° about an axis of rotation indicated by the reference letter “A”. In the present embodiment, the surface 40 has a portion of the mating guide and advancement structure thereon which in the illustrated embodiment is a thread 41 that mates with the partial thread 29 on the bone screw 5 and biases the closure 6 forward due to interaction of the threads 29 and 41 upon clockwise rotation of the closure 6. As noted before, this function can be provided by alternative types of threads or other non threaded structures such as a helically wound flange that slidably mates with a similar structure on the bone screw 5. In the illustrated embodiment the threaded surface 40 has a threadform located thereon that entirely encircles the outer surface 40 of the body 35 and extends entirely from top to bottom. The surface 40 is provided with a thread 41 that is sized, shaped and configured to threadably mate with the threaded surfaces 26 and 27 of the arms 21 and 22, so that the closure body 35 may be threaded into the bone screw head 13, as is shown in FIG. 2.

The closure body 35 also includes at least one removal aperture and in the illustrated embodiment such an aperture is provided by three bores 44, 45 and 46 that are aligned to be parallel with the axis of rotation. The bores 44, 45 and 46 are spaced both from the axis of rotation A and from a periphery 48 of a top 49 of the body. The bores 44, 45 and 46 extend from the body top 49 to a bottom surface 50 of the body 35 in the illustrated embodiment. Preferably the bores 44, 45 and 46 are equally spaced from one another and are approximately equally radially spaced outward from the axis of rotation A. In the illustrated embodiment, the bores 44, 45 and 46 are spaced at approximately 120° from one another. While three cylindrical bores are shown and function as the removal aperture in the illustrated embodiment, it is foreseen that various numbers of openings could be equivalently used and/or such apertures may be of various shapes, such as round, square or kidney bean in cross section, and may be pass through from top 49 to bottom surface 50 of the closure 6 or may just pass through the top 49 thereof and extend partially therethrough.

The break-off head 36 includes a neck 54 that joins with the body top 49 at a torque limiting region or break-off location 56. Preferably the break-off location 56 is generally coplanar with the body top 49, so the break-off location 56 is clean and low profile after such breakoff. The break-off location 56 is normally determined by the location whereat the neck 54 is smallest in cross-section or the location 56 can be triggered by an external groove and other devices known for this purpose. The neck 54 also converges somewhat from the remainder of the break-off head 36 to the break-off location 56.

The break-off head 36 includes a number of facets or panels 60 which are aligned to be parallel to the axis of rotation A and which are joined together to form a polyhedral shaped surface 61 typically associated with a structure to be received in a socket-type tool. The combined surface 61 of the facets 60 forms such a polyhedral shape. A top surface 63 of the break-off head 36 has axially located therein a non-threaded bore 65 for operably receiving a tool during implantation. The bottom surface 50 of the body 35 includes a conical shaped and axially aligned point 67 for engaging and preferably biting into the rod 7, so as to provide an improved grip on the rod to prevent rotation or axial movement thereof relative to the bone screw 5. It is foreseen that the bottom surface 50 may be flat or otherwise shaped and may include other structure to increase frictional engagement between the closure 6 and the rod 7, such as: knurling; a ring with a sharp lower edge, especially when used in conjunction with and surrounding the point 67; or the like.

A tool 70 is illustrated in FIG. 2 for cooperatively inserting the closure 6 into the bone screw head 13. The tool 70 has an elongate shank 71 with a handle 72 sized and shaped to allow a user to rotate the tool 70 clockwise about the axis of rotation A associated with the closure 6. The tool 70 also has a socket type head 74 opposite the handle 72 that is sized and shaped to snugly receive the outer surface 61 of the break off head 36 as is shown in FIG. 2.

During assembly, the rod 7, which is elongate and generally circular in cross-section, is placed within the bone screw channel 23 and the closure 6 is then threaded into the bone screw head 13. The tool 70 is used to rotate the closure 6 until it engages the rod 7 and urges the rod 7 to seat tightly and snugly on the bone screw head base 20 at the bottom of the channel 23. The point 67 engages and digs into the rod 7. As additional torque is applied to the tool 70, a preselected torque is eventually reached (for example 90 inch pounds) whereat the break-off head 36 breaks from the closure body 35 at the break-off location 56 and separates therefrom, such as is shown in FIG. 3.

FIGS. 3 and 4 illustrate the closure 6 operably positioned within the bone screw head 13. FIG. 5 illustrates the closure 6 with the break-off head 36 removed, but shown in phantom to illustrate the position of the break-off head 36 relative to the bores 44, 45 and 46.

In certain circumstances, it is necessary to remove the closure 6 to readjust the position of the rod 7 or to make some other change in the implant 1 configuration. As mentioned before, the implant 1 is typically a part of an overall system and is normally used to provide support to damaged, injured or missing vertebra of the spinal column. When it is necessary to readjust the overall system, the closure 6 is removed by utilization of the second tool 78. The tool 78 includes a shank 80 that has an axis of rotation during use that is coaxial with the axis of rotation A of the closure 6. The shank 80 is attached at one end to a handle 81 to provide a grasp and a means of turning the tool 78 by a user. Opposite the handle 81, the shank 80 has a flat surface 83 from which three pegs or posts 84, 85 and 86 project.

The posts 84, 85 and 86 are parallel to the axis of rotation of the tool 78 and are sized, shaped and positioned so as to be snugly receivable in the closure bores 44, 45 and 46, subsequent to removal of the break-off head 36. The tool 78 is shown in position above the closure body 35 in FIG. 7 just prior to insertion of the posts 84, 85 and 86 into respective bores 44, 45 and 46. The tool 78 is shown positioned with the posts 84, 85 and 86 in the respective bores 44, 45 and 46 in FIG. 8. The purpose of the tool 70 is to allow a user to rotate the closure body 35 counter-clockwise and remove the body 35 from the bone screw head 13 after the closure 6 has been seated therein. In this way the channel 23 can be reopened and the rod 7 removed or repositioned relative to the bone screw head 13.

While the non-axially located bores 44, 45 and 46 of the present embodiment are located between the break-off head neck 54 and the periphery 48, it is foreseen that one or more non-axial bores of this type could partially or entirely intersect with the neck 54 so as to become fully open or exposed at the closure top surface 49 only when a break-off head associated with such a neck breaks from the closure body.

It is to be understood that while certain forms of the present invention have been illustrated and described herein, it is not to be limited to the specific forms or arrangement of parts described and shown. 

1-10. (canceled)
 11. A closure for operably closing a top portion of a rod receiving channel between two arms of a bone anchor, the closure comprising: a) a body with a radially outer surface that is threaded, a top surface, a bottom surface, a central bore that is threaded extending between the top surface and the bottom surface about a central axis, and a drive structure located on the top surface that is positioned between the central axis and the outer surface; and b) a set screw with a radially outer surface that is continuously threaded from near a top surface to near a bottom surface thereof, the bottom surface configured to engage and lock a rod.
 12. The closure according to claim 11, wherein the set screw and the body of the closure are positioned between a pair of top surfaces of the two arms of the bone anchor, so as to provide a comparatively low profile with respect to the pair of top surfaces of the bone anchor arms.
 13. The closure according to claim 11, wherein the drive structure is a bore opening onto the top surface and being spaced from the central axis and the outer surface.
 14. The closure according to claim 13, wherein the closure comprises a plurality of drive structure bores, each being spaced from the central bore and outer surface.
 15. The closure according to claim 11, wherein the closure comprises a plurality of drive structures, each being spaced from the central bore and outer surface.
 16. The closure according to claim 11, wherein the set screw bottom surface is flat.
 17. The closure according to claim 11, wherein the set screw and the body of the closure do not extend above the bone anchor arms. 